The ear first appears in the 3rd week of gestation and it becomes functional by the 16th week. The fetus begins active listening by the 24th week. It is known from ultrasound observations that the fetus hears and responds to a sound pulse starting about 16 weeks of age. This is even before the ear construction is complete. The cochlear structures of the ear appear to function by the 20th week and mature synapses have been found between the 24th and 28th weeks. The sense of hearing is probably the most developed of all the senses before birth. The powerful connection between sound/music and prenatal memory/learning has been revealed in formal experiments, parental observations, clinical records, and first person reports.
As can be seen, there is a need for a safe and comfortable apparatus to deliver sound to prenatal babies.